This will tell your physician whether the goitre has caused any narrowing of the windpipe or if there is an extension into the chest (retrosternal goitre). Interestingly the degree of windpipe (tracheal)displacement does not always correspond to the extent of narrowing or airway obstruction.If there is a suggestion of a retrosternal goitre a CT scan of the neck and chest or an MRI of these areas may be performed.
A CT scan of huge goitre - click to enlarge
This test does not use X-Rays and can demonstrate the structure of the thyroid. It can distinguish cysts from solid nodules but cannot distinguish cancers from innocent nodules (benign nodules). However certain features such as "comet tails" are suggestive of a benign nodule. The size of the nodule is not a indication the the lesion is non malignant. One retrospective study of 207 patients in 1993 who had 472 biopsies found that the risk of malignancy was 21% in patients with nodules less than 1cm but lower at 17% in patients whose nodule was 1cm or greater in diameter. Size is also not a good indicator of the aggressiveness of malignant thyroid nodules. Studies have shown that 35% of tumours of 8-15 mms in diameter had spread outside the capsule while 19% had spread to local lymph nodes. Coarse calcification like comet tails suggests the lesion is non malignant while microcalcification, lack of a distinct margin, and a high blood flow within the nodule is suggestive of malignancy.These facts emphasize how difficult it is to manage the small incidental thyroid nodule. These lesions are very common but should be assessed in high risk groups by fna and a watch policy. The British Thyroid Association recommends that incidental none palpable thyroid lesions 1cm or less may be managed in primary care. The American Thyroid Association guidelines suggest that such patients need no futher work up and can be discharged even from primary care. My own view is that when detected such small lesions should be subjected to yearly ultrasound for 5 years and if stable this is an indicator of no malignancy. Remember that 1 in 5 patients benign nodules grow in size within 2 years so growth does not mean cancer! A novel use of ultrasound is the assessment of the vocal folds prior to surgery. The assessment of the vocal fold is possible by ultrasound but may be hindered by calcified thyroid cartilages.
This test must not be used in pregnancy. It is useful in a thyrotoxic patient where it shows the extent of the over activity in the thyroid. Nodules that take up radioactivity are rarely cancerous though this is not impossible. The use of radioactive scans is limited in the UK to thyroid cancer patients. In the USA radioactive scanning is used in THY3 lesions. The American rationale is that if the THY 3 lesion (a suspicious or follicular lesion) is hot on the scan that surgery is not indicated as the risk of thyroid cancer is very small. This not the British practice because malignancy can occur even in hot lesions and one historical report suggested a risk of malignancy of up to 6%!
A hot nodule. (This the black rounded area on the left side of the scan picture it is in the patients right lobe of thyroid) - click to enlarge
These may be necessary in retrosternal goitre to separate local pressure effects, caused by the goitre, from hidden asthma. The common method used is a flow volume loop.The correct diagnosis is essential because simple thyroid surgery, if the thyroid is at fault, will cure breathing problems. In extrathoracic obstruction the flow volume loop is changed and the inspiratory airflow is reduced whereas in asthma the expiratory air flow is reduced.
The extent of tracheal displacement does not relate well to the degree of airway obstruction. If there is a 75% reduction in the cross-sectional area of the trachea however, then noisy breathing (stridor) may occur.
The activity of the thyroid can be checked by performing tests of iodothyronine levels (T4 and T3) and the pituitary influence on the thyroid (TSH). In over activity, the T3 and T4 are high and the TSH is lower than normal. Rarely the T4 is normal while the T3 is raised with a low TSH (T3 thyrotoxicosis). A large prospective study has shown that patients with a high TSH have a 11 times higher incidence of thyroid cancer when compared with patients whose TSH is within the reference range. This high incidence of cancer most likely is due to the very high number of patients in the raised TSH group with Hashimoto's thyroiditis. Hashimoto's thyroiditis is known to be associated with thyroid cancer and lymphoma. The calcium level checks the status of the parathyroid glands. If the calcium is abnormal a blood parathyroid test (PTH) is performed. There ia an association of thyroid cancer and parathyroid tumours particularly in patients with a history of neck irradiation. The complication of a low calcium level occurs in 30% of patients undergoing a total thyroidectomy. One cause of this is a low pre-operative vitamin D level. All patients undergoing a subtotal or total thyroidectomy should have their pre-operative vitamin D status checked and made if possible vitamin d replete.The immune status of the thyroid may be checked (thyroid antibodies). This may help to predict the need for thyroid replacement following a partial thyroidectomy.
Unless there are special circumstances, all single nodules in the thyroid should be subjected to a fine needle aspiration (FNA). This test is similar to a blood test and involves needling the thyroid. It is not 100% accurate. It has two roles: it can be therapeutic, in the case of a simple cyst which may be aspirated to dryness and avoid the need for surgery, or diagnostic in differentiating cancers from innocent nodules.
Fine needle aspiration results should be viewed with a cynical eye. The test is of no value in separating cancers from innocent nodules in follicular lesions. If the FNA is used as a means of separating a benign from a malignant lesion, and no surgery is undertaken, it is essential that the test is repeated within 6 months and, if negative for cancer, again in a year. Fine needle aspiration should be combined with ultrasound to allow accurate sampling of different areas of the thyroid mass. This is particularly important in large cystic masses as it allows any suspicious areas of the cyst wall to be biopsied.
In the case of lymphoma of the thyroid, it is usually necessary to do core biopsy which is similar to an FNA but uses a larger diameter needle. This latter procedure is usually carried out under local anaesthetic.
Please see the introduction section of thyroid surgery where the results of FNA of the thyroid are discussed in detail.
It is valuable for the surgeon to get an independent assessment of the throat pre-operatively. This test is mandatory when there is a suggestion of voice change, a positive fine needle biopsy for cancer, or there has been previous thyroid surgery. The use of voice box assessment is discussed in detail by our ENT specialist Mr Will Grant, in the section entitled Thyroid and the Voice.